The present invention is related to a system and method for candidate line segment generation, and to a solid model synthesis system and method. More particularly, the invention is a system for extracting candidate line segments and a candidate line segment generation method for extracting, from a first drawing and a second drawing of a solid (which are made by projecting a solid onto two planes perpendicular to each other) candidate line segments for forming a third drawing made by projecting the solid onto a plane perpendicular to each of the two planes, and to a solid model synthesis system and a solid model synthesis method for synthesizing a three-dimensional solid model, from the first and second drawings and from the third drawing made by the candidate line segments.
Many manufacturers have been making drawings for design, and have been accumulating design information in the form of drawings.
However, recently, the improvement of simulation techniques and numerical control (NC) techniques has enabled the functions of an object of design to be evaluated on a computer, allowing creation of an actual prototype by transferring data to a machine tool. In this case, two-dimensional drawings are insufficient, and a solid, three-dimensional model is required. Accordingly, in recent years, three-dimensional models are often used, which store data of solids, faces, edges, and vertices in the form of a table, and have various functions such as a wire frame model display function and a surface model display function.
However, most of the conventional design information is saved in the form of drawings such as a front view, a top view, and a side view. Consequently, to evaluate the functions of an object of design on a computer, it is necessary to synthesize a solid model from such plurality of drawings in which the design information is held, but the synthesis of a solid model takes tremendous time and labor. For this, various studies have been made on a method for synthesizing a solid model from a plurality of drawings, and various solid model synthesis systems as described below have been provided.
That is, a solid model synthesis system is provided (Japanese patent number 6-119463, U.S. Pat. No. 6,078,330) in which the shape of a solid model is input in the form of three views, a front view, a top view, and a side view, to synthesize a solid model corresponding to the three views. The solid model synthesis system is characterized by having a means for obtaining, from the two-dimensional data of vertices and line segments of the figures given as the above three views, the three-dimensional data of three-dimensional line segments forming the wire frame of a solid corresponding to the figures, and further by having a means for dividing the respective regions defined by the plurality of three-dimensional line segments into cells having a boundary surface and a volume, and a means for holding the cells obtained by the division as a non-polyhedral data structure, respectively, together with a means for evaluating whether or not there is an inconsistency in the adjacency relationship between the cells with reference to the three views, and a means for synthesizing a solid model by constructing each cell based on the combination of consistent cells.
Further, the present applicant already proposed a solid model synthesis system for synthesizing a solid model from a plurality of incomplete drawings (Japanese Patent No. 5-184244). This solid model synthesis system calculates the line segments from each drawing of the plurality of incomplete drawings, constructs a wire frame model based on the calculated line segments and compares the edges of the constructed wire frame model with the line segments to correct the wire frame model. Then the corrected wire frame model is transformed to a cell division model. In addition, a condition for at least one of the three views to be correct is set by a Boolean question, and a combination of cells, which is the solution of this equation, is determined, and a solid model is synthesized based on the combination of cells.
Furthermore, the present applicant already proposed a solid model synthesis system for synthesizing a solid model from one top view and one or more sectional views(Japanese Patent Number 5-245384, U.S. Pat. No. 5,171,553). In this solid model synthesis system, input two-dimensional drawing data is classified into top view data and sectional view data. Closed regions, and the inclusion relationships between the respective closed regions, are detected from the top view data, and the attributes of the detected closed regions of the same attribute are grouped. The sectional view data is divided based on the data of the detected closed regions, and the closed regions are made three-dimensional based on the divided sectional view data. Then, of the closed regions other than the closed regions made three-dimensional, those which belong to the same group as the closed regions made three-dimensional are made three-dimensional in the same manner as the closed regions made three-dimensional. Then, based on the inclusion relationships between the respective closed regions, a solid model is synthesized by combining the respective closed regions by a set operation.
The basic method for synthesizing a solid model employed in the above various solid model synthesis systems uses the method proposed in xe2x80x9cConstruction of a Solid Model Using Orthographic Views with Focus on Polyhedraxe2x80x9d (Information Processing, Vol. 31, No. 8, Ito Kiyoshi, 1990). In this method, first the data of three views is input, and by selecting, from the respective vertices of the three views, a combination of vertices which can be vertices on three-dimensional coordinates, thereby to synthesize three-dimensional candidate vertices. If the projection view of a line segment connecting two candidate vertices among these candidate vertices appears in all of the given three views as vertices or line segments, and no other candidate vertex exists between the two candidate vertices, then the particular line segment is held as a candidate edge. Then, a face surrounded by candidate edges on the same plane and containing therein no other candidate edge is held as a candidate face. Next, for instance, using the knowledge about a three-dimensional shape such as xe2x80x9cAll candidate vertices and candidate edges are boundaries of a candidate face,xe2x80x9d candidate vertices and candidate edges such as isolated points and hanging edges, which are inconsistent as structural elements of a solid model, are removed. Subsequently, a set of candidate faces which can be the boundaries of a solid model are searched for. Since a solid model has the restriction that every edge is shared by only two faces and structural elements do not intersect each other except on a boundary, all sets fulfilling such condition are determined, and the set of the obtained faces forms a solid model.
However, for a relatively simple design plan, only two views, a top view and a front view, may be made for convenience sake. In such case, a computer can e used to automatically make a side view from the top and front views which have already been made, and from the three views, the top, front, and side views, a solid model can be synthesized using various solid model synthesis systems as described above.
In the process step for automatically extracting candidate line segments from the top and front views in the above solid model synthesis process, the two-dimensional coordinates (Xt, Yt) of a vertex P on the top view and the two-dimensional coordinates (Xf, Yf) of a vertex Q on the front view are extracted, and a candidate vertex of the side view is determined according to a rule that a vertex R of the two-dimensional coordinates (Yt, Yf) is generated on the side view when Xt=Xf is valid, and if line segments corresponding to the line segment connecting two candidate vertices exist in the top and front views, the line segments connecting the two candidate vertices is determined to be a candidate line segment of the side view. For instance, as shown in FIG. 13, from two views in which a top view 70 and a front view 72 are both square, the four sides and the diagonal lines 76 and 78 of a square are extracted as the candidate line segments of a side view 74.
However, such a conventional candidate line segment extraction method caused the inconvenience that the number of the candidate line segments of the side view became considerably large and the time taken for the process for synthesizing a solid model greatly increased. For instance, for the process for extracting the candidate line segments of the side view from a top view 80 and a front view 82 shown in FIG. 14 which are relatively complicated, a resultant side view 84 contained a large number of candidate line segments, and a considerable amount of time was required to process them.
Accordingly, in view of the above fact, it is the first object of the present invention to provide a drawing candidate line segments extraction system and a drawing candidate line segments extraction method, in which only proper candidate line segments can be extracted from two drawings as the candidate line segments for a third drawing.
In addition, it is the second object to provide a solid model synthesis system and a solid model synthesis method, in which the extracted proper line segments are used to make the third drawing thereby for synthesizing a solid model.
To accomplish these objects, and other objects as set forth more particularly in the claims, the drawing candidate line segment extraction system extracts, from a first drawing and a second drawing which are made by projecting a solid onto two planes perpendicular to each other, candidate line segments which are the candidates for line segments forming a third drawing made by projecting the solid onto a plane perpendicular to each of the two planes, characterized by comprising: a coordinate extraction means for extracting the two-dimensional coordinates of the points corresponding to vertices of the solid in each of the first the second drawings, a candidate vertices generation means for comparing the two-dimensional coordinates of the first drawing extracted by the coordinate extraction means and the two-dimensional coordinates of the second drawing extracted by the coordinates extraction means and, if the values of one coordinate determined by the relationship between the first and second drawings are equal, generating the combination of the values of the respective other coordinate as the two dimensional coordinates of candidate vertices in the third drawing, and a candidate line segment extraction means for extracting the line segments formed by connecting two candidate vertices of the candidate vertices generated by the candidate vertices generation means as candidate line segment for the third drawing in at least one of the following cases:
(1) a case in which the line segments formed by connecting two candidate vertices are horizontal or vertical in the third drawing, and line segments corresponding to the particular line segments exist in the first and second drawing, and
(2) a case in which the line segments formed by connecting two vertices are not horizontal or vertical in the third drawing, line segments corresponding to the particular line segments exist in the first and second drawings, and the link segments existing in the first and second drawings are not horizontal or vertical.
To accomplish the above second object, the solid model synthesis system is characterized by comprising: a coordinate extraction means for extracting the two-dimensional coordinates of the points corresponding to vertices of a solid in each of a first drawing and a second drawing which are made by projecting the solid onto two planes perpendicular to each other, a candidate vertices generation means for comparing the two-dimensional coordinates of the first drawing extracted by the coordinate extraction means and the two-dimensional coordinates of the second drawing extracted by the coordinate extraction means and, if the values of one coordinate determined by the relationship between the first and second drawings are equal, generating the combination of the values of the respective other coordinate as the two-dimensional coordinates of candidate vertices in a third drawing generated by projecting the solid onto a plane perpendicular to each of the two planes, a candidate line segment extraction means for extracting the line segment formed by connecting two candidate vertices of the candidate vertices generated by the candidate vertices generation means as candidate line segment for the third drawing at least in one of the following cases:
(1) a case in which the line segments formed by connecting two candidate vertices are horizontal or vertical in the third drawing, and line segments corresponding to the particular line segments exist in the first and second drawings, and
(2) a case in which the line segments formed by connecting two candidate vertices are not horizontal or vertical in the third drawing, and line segments corresponding to the particular line segments exist in the first and second drawings, and the line segments existing in the first and second drawings are not horizontal or vertical, a composition means for making the third drawing from the line segments which are extracted by the candidate line segments extraction means and forming the third drawing, and a solid model synthesis means for synthesizing a solid model which is a three-dimensional model, based on the first and second drawings, and the third drawing made by the composition means.
To accomplish the above second object, the solid model synthesis method is characterized in that the first and second drawings are a top view and a front view, respectively.